1) Field of the Invention
The present invention is a device and supporting assembly for measuring electrical properties over a range of frequencies for a dielectric material in which surface contours of the material are concave or convex.
2) Description of the Prior Art
The nondestructive measurement of insulating materials includes using an open-ended coaxial probe. The coaxial probe is unique among techniques for measuring the dielectric properties of materials. Because the open-ended coaxial probe uses a non-invasive method that only requires contact with a material sample; the probe can characterize properties over a broad range of frequencies.
In Rivera (U.S. Pat. No. 7,495,454), a coaxial probe comprises two components. One component is a section of open coaxial line attached to a conducting flange. When placed firmly against the dielectric material of an insulator; the probe determines a relative permittivity as a function of frequency from measurements that includes a complex reflection coefficient.
The open-ended coaxial probe relies on a testing surface in which the surface is relatively flat and smooth. When the probe is placed on a surface which is not flat; errors result because of air gaps between the aperture surface and the sample. To accurately account for the presence of air gaps, computer modeling methods are required to fully represent the electromagnetic fields within the material and in the air gap region.
Examples exist for measuring the dielectric properties of a curved dielectric surface. In a prior art device, a center conductor of a probe extends to contact the material and minimize the air gap. A finite-element method is used; thereby, requiring the probe and dielectric surface to be accurately modeled. This is disadvantageous because coaxial probes are non-standard devices which could have any size; thereby, requiring a time-consuming effort for modeling varying sizes and shapes.
As such, a need exists for a probe which can contact varying surfaces such as a convex or concave dielectric surface without air gaps.